Refrigeration by direct vapor condensation

ABSTRACT

915,413. Storing liquefied gases. CHICAGO BRIDGE &amp; IRON CO. July 19, 1961 [Dec. 23, 1960]. No. 26076/61. Class 8(2). A vapour relief duct 26 of a heat insulated liquefied gas e.g. butane container 10 is surrounded by a condenser 20 down which passes liquefied gas having been withdrawn from the container by a pump 17 and sub-cooled in an exchanger 14 itself cooled by external refrigeration system 11-13. Any uncondensed low boiling impurities are discharged to atmosphere through a purge line 32, Fig. 2 (not shown).

J. B. MAHER ETAL. REFRIGERATION BY DIRECT VAPOR CONDENSATIQN Oct. 29, 1963 Filed Dec. 25, 1 960 i Hm W Q Q\ I H. m W Eu r in w m \w "W k N N RN wN In in I,

United States Patent 3,198,447 REFRIGERATION BY DIRECT VAPOR CONDENSATION James B. Maker and James Mair, Chicago, 111., assignors to Chicago Bridge & Ironv Company, Chicago, Ill. Filed Dec. 23, was, Ser. No. 7 8,07 5 Claims. (Cl. 62--54) This invention relates to the refrigerated storage of a liquefied normally gaseous product. It more particularly relates to controlling the vapor pressure of the stored liquid product by direct vapor condensation.

It is well known in the art that for liquids whose vapor pressure is greater than one atmosphere at normal atmospheric temperature, a refrigerated tank provides an efficient storage facility. Insulation of the storage tank is necessary and refrigeration equipment must be provided to remove the heat introduced by (a) heat leak into the tank from the surrounding atmosphere and (b) heat introduced as sensible heat in the filling stream entering the tank.

When the stored liquid product is relatively pure and ubstantially free of constituents having a lower boiling point than the stored product, the refrigeration can be eifected by withdrawing vaporous product efliuent from the tank by a compressor, compressing it to a point at which it may be condensed by cooling with ambient air or available water, and returning the condensed liquid to the storage tank wherein it is fiash-vaporized at storage conditions. The refrigeration effect produced by this conventional vapor compression refrigeration system maintains the stored product at design temperature. This method is also referred to :as self-refrigeration or open cycle refrigeration.

If, however, the stored liquid product contains a 0.5% to 5.0% or more of constituents having a lower boiling point than the stored liquid, these constituents will appear as non-condensable gases at the temperature and pressure prevailing in the condenser, eventually raising the backpressure on the compressor until the refrigeration system becomes inoperative. In such cases, and es ecially when the stored liquid product is a mixture of components having different boiling points, it is necessary to resort to closed-cycle refrigeration.

In closed-cycle refrigeration the stored liquid is withdrawn from the tank, cooled in a heat exchanger, and returned to the tank. Experience has shown that it is very difficult to control the vapor pressure in the tank by this method, because:

(a) There are zones of varying temperature throughout the storage tank;

(1)) The cooling and condensing eifect of the liquid surface on the vapor in the vapor space is slow and delayed;

(0) Even if the cold returned liquid is sprayed into the vapor space, low contact time and limited dispersion affect the rate of vapor condensation.

In accordance with this invention, there is provided an apparatus and a method employing a closed-cycle refrigeration system whereby the tank pressure can be con trolled without heating or further vaporizing the product by the recirculated stored liquid thereby limiting the release of vapor not condensable in the main refrigeration condenser.

Referring to the drawings:

FIGURE 1 is a schematic flow diagram of a refrigeration system employed in the instant invention.

3 1%,447 Patented Oct. 29, 1963 FIGURE 2 is a schematic cross-sectional elevation view of a direct contact condenser used for effecting an intimate contact between the recycled cooled product and the Vaporous efiluent from the storage system.

FIGURE 3 is an enlarged cross-sectional view taken along line 3-3 of FIGURE 2 to illustrate the mounting arrangement for the condenser vapor tube.

In FIGURE 1, there is diagrammatically illustra ed an illustrative embodiment of the refrigeration storage system which comprises a conventional fiat-bottom insulated tank 10, which is used to store the product. Because tank It is not completely filled with liquid product there exists a vapor space V above the liquid. To effect the refrigeration of the stored product, there is also provided a refrigeration system which comprises a conventional refrigerator 11 which cools a heat exchanger fluid which circulates through lines 12 and 13 to heat exchanger 14. In the exchanger 14 the liquid L is sub-cooled after being drawn from the tank 16 through line 15 and -16 by means of pump 17 which circulates liquid L from the heat exchanger 14 by way of line 18 to the direct condenser Ztl, from which it returns to the storage tank by gravity.

Referring to FIGURE 2, there is shown a direct contact condense-r 2i connected to the top of tank it} by means of flanged nozzle 19. As illustrated, the condenser 26 comprises a chamber 21 in which is arranged a series of b aille trays 2d and 23 and a diffuser baflle 24. Bafiles 22 are annular discs having a central opening 25. The discs are attached to the wall of chamber 21. Bathe trays 23 having a smaller outer diameter than the internal diameter of chamber 21 are mounted on a vapor pipe 26 which is coaxially suspended within chamber 21 by means of suitable spider arms 2''] which radially extend from bafile trays 23 and are fastened to the wall of chamber 21. Diffuser bathe 24 which serves to prevent the flow of circulating liquid L directly in vapor pipe 26, and distribute the liquid over the interior of the chamber is suspended iron-1 the domed chamber end closure 28 by means of hangers 29. Vapor pipe 26 which extends into the vapor space V of tank It} is provided with perpendicularly extending vapor withdrawal side arms '30 and 31 which improves the vapor gathering efliciency of the vapor withdrawal means. A purge line "32 is used to remove any non-condensables which accumulates from time to time in the condenser 2i) and pass them, for example, to a suitable flare, not shown.

In operation, the sub-cooled circulating liquid L discharging from line 15 enters the condenser 20 wherein it is distributed by bafiie 24 and cascades over the series of alternating baflle trays 22 and 25 which are alternately arranged in the condenser chamber 21 to provide maximum contact time and surface between the liquid and vapor. The T-shaped vapor withdrawal means withdraws product vapor including non-condensables from the vapor space to replace vapor condensed in the condenser 20. Most of the low boiling point constituents or non condensables present in the vapor space are also condensed or are carried by entrainment back to the vapor space through the annulus between the vapor pipe 25 and the mounting nozzle 19 on tank iii. The small amount of non-condensables which do not return to the storage tank accumulate in the dome of condenser 29 from whence they can be removed from time to time through line 32.

In condenser 20 the bafiie trays 22 depend inwardly from the side wall of condenser 20 and the baflle trays 23 are supported by the vapor inlet pipe 26, which also conducts vapor gathered from the vapor space to the top of the condenser 20. With this arrangement, only one mounting nozzle 19 functioning as vapor inlet, condensate outlet, and vent gas outlet is required.

In an arrangement such as shown in FIGURE 1, a conventional, insulated, double-wall, fiat bottom cylindrical 50-barrel storage tank storing liquid n-butane, containing 2% of propane as non-condensable, at 30 F. and 0.5 p.s.i.g. can be used. The required inner storage vessel is 80 feet in diameter and 56 feet high. The tank is covered with inches of Foarnglas or other suitable insulating material. Accordingly the refrigeration system must compensate for a warming up of the liquid, L, of 120,000 B.t.u.s per hour. In this example, 35 gallons per minute, or 10,300 pounds per hour, of the n-butane are withdrawn by a suitable pump and cooled in a heat exchanger. In the heat exchanger the temperature of the n-butane is cooled from the 30 F. storage temperature to F. by conventional, indirect, heat-exchange, refrigeration apparatus. The sub-cooled n-butane is circulated into a direct contact cascade condenser of the type illustrated in FIGURE 2 which is mounted atop the storage tank from which it discharges into the vapor space. The recirculated n-butane condenses 560 pounds per hour of the Warmer vapor in the condenser while reaching an equilibrium temperature of 25 F. Both the recirculated n-butane and the condensed vapor re-enter the tank, and additionally cool the stored n-butane until the resulting equilibrium temperature of 30 F. storage temperature is reached by the returning liquid. The total refrigeration effect of the continuous recirculation system is 120,000 B.t.u.s per hour, as was required.

This invention offers the following advantage (1) l ressure control is eifected by manipulating the product in the vapor phase insuring fast, accurate response to signals from a controller used to control the flow of circulating refrigerated stored product.

(2) At no point in the product cycle is the product exposed to a higher temperature.

(3) Product is not vaporized and condensed in the refrigeration cycle, the only vaporization is that due to heat leak and this vapor is immediately condensed by sub-cooled product.

(4) Product vapor is condensed at storage temperature and pressure by intimate contact with sub-cooled product liquid.

(5) The condenser has no tubes or heat transfer surface which could become fouled and require maintenance.

(6) The design of the concentric vapor inlet to the condenser enables the condenser to bring in a continuous stream of vapor from the storage tank to be purged of lower boiling constituents by entrainment through the annular space around the vapor pipe.

(7) The device is simple in design, requires no maintenance, and mounts directly on the storage vessel.

While some storage facilities include tanks in which the product is held at close to atmospheric pressure, others are operated at temperatures which correspond to pressures above or below atmospheric. Being completely sealed, this invention is applicable to any refrigeration storage system at any pressure.

The instant invention has especial application in the refrigerated storage at temperatures within the range of about 10 to 40 F. of liquefied materials such as C -C hydrocarbons such as ethylene, butadiene, iso-butane, chlorine, ethyl chloride, vinyl chloride, ethylene oxide, ammonia, etc., containing more than about 0.5% noncondensables. Other products and other storage conditions, however, can be used. It can be employed in storage facilities where 10,000 to 6,000,000 gallons per tank of liquid material are stored. Conventional materials of construction and equipment are utilized in assembling the storage system of this invention. The refrigeration system employed to cool the recirculated liquid material .should have sufiicient capacity to sub-cool it at least F.

4 below storage conditions. Because there is no compression cycle, the non-condensates do not interfere with the operation of this refrigeration system as they do in conventional refrigeration systems.

The liquid vapor contact apparatus employed to condense the vapor withdrawn from the vapor space should have sufficient contact area provided to condense substantially all of the vapor withdrawn in the condenser chamber. Other types of cascade contact apparatus as well as other liquid-vapor contact equipment such as bubble towers, etc., can be used. Such modifications and variations Will be apparent to those skilled in this art without the exercise of inventive facilities.

Accordingly, the specific examples used herein were given for clearness of understanding only and no undue limitations thereon should be implied.

What is claimed is:

1. A refrigerated storage system for the storage of liquid, normally gaseous products, said system comprising:

a liquid product storage tank having a liquid product zone and a vapor zone;

means connected to said tank for removing a portion of said liquid product;

refrigeration means connected to said liquid product removal means for reducing the temperature of said portion of liquid product;

and a vapor-liquid contactor located above said tank,

closed to the ambient atmosphere, and disposed between and in communication with said vapor zone and said refrigeration means for bringing said refrigerated portion of liquid product into intimate contact with vapor withdrawn from said vapor zone into said contactor, said contactor including:

a vertically disposed chamber portion;

an outlet at the top of said chamber for removing accumulated non-condensable vapors;

flow control means on said outlet;

pipe means for conducting vapor from said vapor zone in said tank, said pipe means having a vapor withdrawing portion depending from said chamber into said vapor zone and a remaining portion extending upwardly within said chamber, substantially coextensive therewith, and terminating at an upper open- 111g;

liquid product inlet means in communication with said refrigeration means for receiving said cooled liquid product portion, said inlet means being located to direct refrigerated liquid downwardly from the top of said chamber portion through said chamber portion;

and vapor-liquid bafile means disposed between said upper opening in the vapor conducting pipe means and said liquid product inlet means for providing concurrent contact between said vapor and sad liquid at the top of said chamber portion and for preventing entry of liquid into said pipe means.

2. In a system in accordance with claim 1 in which the said contactor is mounted directly atop the vessel to which the condensate is to be returned.

3. In a system in accordance with claim 1 in which said withdrawing portion of said vapor inlet means includes means extending laterally from said depending portion into said vapor zone for facilitating the withdrawal of vapor from said vapor zone.

4. In a system in accordance with claim 2 in which said contactor comprises: a direct contact, cascade condenser having said vapor conducting pipe means depending into said vapor zone and being concentrically mounted within said condenser; said condenser further having a plurality of cascade trays mounted on said pipe means and an alternating plurality of cascade trays mounted on said condenser.

5. In a system in accordance with claim 4 in which said direct contact cascade condenser has said pipe means, a condensate outlet, and a vent gas outlet incorporated References Cited in the file of this patent UNITED STATES PATENTS McCreery June '26, 1900 6 Wilton July 19, 1932 Gibson Nov. 3, 1936 Buehler Dec. 1, 1936 Dennis Feb. 15, 1944 Brandon Ian. 31, 1956 Etienne Aug. 25, 1959 Basore et a1. July 12, 1960 

1. A REFRIGERATED STORAGE SYSTEM FOR THE STORAGE OF LIQUID, NORMALLY GASEOUS PRODUCTS, SAID SYSTEM COMPRISING: A LIQUID PRODUCT STORAGE TANK HAVING A LIQUID PRODUCT ZONE AND A VAPOR ZONE; MEANS CONNECTED TO SAID TANK FOR REMOVING A PORTION OF SAID LIQUID PRODUCT; REFRIGERATION MEANS CONNECTED TO SAID LIQUID PRODUCT REMOVAL MEANS FOR REDUCING THE TEMPERATURE OF SAID PORTION OF LIQUID PRODUCT; AND A VAPOR-LIQUID CONTACTOR LOCATED ABOVE SAID TANK, CLOSED TO THE AMBIENT ATMOSPHERE AND DISPOSED BETWEEN AND IN COMMUNICATION WITH SAID VAPOR ZONE AND SAID REFRIGERATION MEANS FOR BRINGING SAID REFRIGERATED PORTION OF LIQUID PRODUCT INTO INTIMATE CONTACT WITH VAPOR WITHDRAWN FROM SAID VAPOR ZONE INTO SAID CONTACTOR, SAID CONTACTOR INCLUDING: A VERTICALLY DISPOSED CHAMBER PORTION; AN OUTLET AT THE TOP OF SAID CHAMBER FOR REMOVING ACCUMULATED NON-CONDENSABLE VAPORS; FLOW CONTROL MEANS ON SAID OUTLET; PIPE MEANS FOR CONDUCTING VAPOR FROM SAID VAPOR ZONE IN SAID TANK, SAID PIPE MEANS HAVING A VAPOR WITHDRAWING PORTION DEPENDING FROM SAID CHAMBER INTO SAID VAPOR ZONE AND A REMAINING PORTION EXTENDING UPWARDLY WITHIN SAID CHAMBER, SUBSTANTIALLY COEXTENSIVE THEREWITH, AND TERMINATING AT AN UPPER OPENING; 